The development of HIV vaccines and other prevention strategies relies on the use of nonhuman primates in preclinical studies to advance the development of effective AIDS vaccine candidates and to advance development of effective topical microbicides and other prevention modalities or immune-based therapies. The NIAID Simian Vaccine Evaluation Unit (SVEU) contracts shall provide nonhuman primate resources that primarily support preclinical evaluation of AIDS vaccines. The SVEUs conduct studies in support of vaccines being developed by a wide range of investigators. These studies complement NIAID-supported basic vaccine research and vaccine evaluation studies funded through R01 (investigator-initiated research) grants, HIVRAD (HIV Vaccine Research and Design Program) grants, IPCAVD (Integrated Preclinical-Clinical AIDS Vaccine Development) grants, and NHP Consortium awards. The SVEUs also perform studies of candidate vaccines offered by companies or other researchers. HIV sequence diversity and potential decoy epitopes are hurdles in the development of an effective AIDS vaccine. Seven conserved elements (CE) have been identified in HIV p24gag and immunogens have been generated and have shown to be immunogenic in mice and macaques.